This invention relates to a method and an apparatus for making wrapper sleeves from preferably heat sealable film sheet lengths by providing thereon a longitudinal seam, particularly a fin seal for bonding together opposite longitudinal edges of the film sheet.
It is known to make wrapper sleeves from individual film lengths. For forming the sleeve, the film length is wrapped around a forming mandrel and a longitudinal seam is formed by means of sealing shoes movable towards one another. In this process it is of advantage to make the forming mandrel part of a mandrel wheel so that the sleeve wrapper packages may be manufactured stepwise in simultaneously operating different stations. This results in a high machine output.
Machines of the above-outlined type have, in particular, two disadvantages which set limits to the machine output: first, the welding of the longitudinal seam is carried out in a station where a necessary dwelling period has to be observed. Second, the machine components have to execute relatively complex motions for wrapping the film material about the forming mandrel. Such machines are disclosed, for example, in Swiss Pat. No. 373,947 and German Auslegeschrift (application published after examination) No. 2,000,570.
According to Swiss Pat. No. 373,947, a wrapper film of cut length is positioned on a table formed of two elements of a forming box and is then brought into the correct position by means of lateral holders. A plunger situated between the two elements is, together with the elements, raised, whereby the film is folded about a mandrel. The edge portions of the film projecting beyond the mandrel are of unequal length. Two heated sealing shoes are pivoted towards one another, whereby the longer edge portion is folded over onto the shorter edge portion in such a manner that the two edge portions may be welded (heat-sealed) to one another. It is a disadvantage of this arrangement that the folding elements have to execute a relatively large stroke and the plunger situated therebetween executes only a small stroke. Further, an additional folding operation has to be performed with one of the sealing shoes. The tip of the sealing shoe with which the longer edge portion is folded lies against the mandrel and thus heats, in addition to the sealing seam, film portions that may be damaged by such a heat effect.
According to German Auslegeschrift No. 2,000,570 the portions of the film to be folded about the mandrel are lifted by pressurized air before folding forks press these film portions against the mandrel. The film edges project freely beyond the folding forks and may flutter in the airstream which may lead to malfunctions. Here too, the sealing shoes may damage portions adjacent the sealing seam in case the seal has to be provided close to the mandrel. In a sleeve package, however, it is of importance that the walls lie fully against the contents so as not to generate the impression of a loose package. For this reason, the welded seam has to provided close to the mandrel.